1. Field of the Invention
The present invention relates to an optical cable, which is formed by laminating together a plurality of optical fiber tape cores, in which multiple optical fiber cores are arrayed in the form of a tape, and housing this laminate inside a sheath; a device for manufacturing this optical cable; and an optical cable production method which employs this manufacturing device.
2. Background Art
Optical cables in which an optical tape core laminate, obtained by arraying multiple optical fiber cores in the form of a tape and laminating a plurality of these optical fiber tape cores together, is housed inside a pipe-shaped sheath, have been disclosed in (1) U.S. Pat. No. 4,744,631, (2) U.S. Pat. No. 5,621,842, and (3) U.S. Pat. No. 6,122,424.
The sheath in these optical cables has been filled with a jelly-like water-repelling blended material or a filling material having elastic properties. An optical cable has also been disclosed in (4) EP 1,085,359A2 in which an optical tape core laminate, that is protected by a protective tape, is covered by a sheath.
In addition, optical cables have been disclosed in (5) Japanese Patent Application, First Publication No. 3-172808, (6) Japanese Patent Application, First Publication No. 4-143710, and (7) Japanese Patent Application, First Publication No. 8-240752, which employ a spacer in which at least one or more spiral grooves (referred to as xe2x80x9cslotsxe2x80x9d hereinafter) are formed in the surface of a long cylindrical rod consisting of a plastic material, and the optical tape core laminate is housed inside this slot. Further, (8) Japanese Patent Application, First Publication No. 2-83507 discloses an optical cable in which an optical fiber tape core laminate is housed inside spiral grooves in a spacer in which the spiral grooves reverse directions alternating from the left to the right, i.e., alternately reverse in the SZ directions, at a fixed cycle on the surface of a cylindrically shaped rod. (9) Japanese Patent Application, First Publication No. 4-182611 discloses an optical cable in which a plurality of optical fiber tape cores are laminated inside a pliable housing member (uni-slot tube) which is shaped in the form of the letter xe2x80x9cUxe2x80x9d in cross-section, and this pliable housing member is twisted in the SZ directions around a tension member.
However, the optical cables disclosed in patent applications (1)xcx9c(3) above employ a relatively large amount of filling material to fill the sheath, so that a spacer for this filling material is needed. Thus, a thicker cable diameter and a heavier cable weight result.
The optical cable disclosed in patent application (4) requires the step of wrapping protective tape around the optical tape core laminate, while the optical cables disclosed in patent applications (5) through (9) require the step of forming the slot in the surface of the cylindrical rod. As a result, a greater number of manufacturing steps are required to produce the optical cable, and there are also disadvantages in terms of costs. Moreover, in the optical cables disclosed in patent applications (5) through (9), distortion in the optical fiber core increases when the optical fiber tape core is mounted inside the slot, so that a cable with excellent properties is not obtained.
In addition, given the size of the distortion that occurs in an optical fiber core housed inside spiral grooves formed in a spacer which reverse from the S direction to the Z direction, and from the Z direction to the S direction, when the optical cable housing this optical fiber core is bent, (10) Japanese Patent Application, (Granted) Publication No. 7-13687 suggests that it is preferable that the track of the spiral grooves be in the form of a sine wave, and the angle of reversing be in the range of 230xc2x0 to 330xc2x0, i.e., the spiral grooves reverse at every 230xc2x0 to 330xc2x0 rotation, with 275xc2x0 providing the smallest distortion in the optical fiber core.
However, to form a spiral groove of this shape requires highly controlled techniques. Moreover, the technique disclosed in (10) is directed to optical cables in which the number of optical fiber cores is in the range of 3000xcx9c4000, or more.
On the other hand, an optical cable having a structure like that shown in FIG. 15 has been proposed recently.
In FIG. 15, numeral 1 indicates an optical tape core laminate in which multiple layers of optical fiber tape cores have been laminated together. This optical tape core laminate 1 is not fixed completely in place inside a forming pipe 2, but rather is housed with an interval of spacing between itself and the forming pipe 2. This forming pipe 2 is formed into the shape of a pipe by employing a pipe-forming method in which tape, consisting of a rigid plastic film like polyester, polypropylene, polyethylene, polyamide, or fiber reinforced plastic (FRP), is continuously fashioned into the shape of a pipe. The seams running along the longitudinal direction of this forming pipe 2 are then joined together by meaning of adhesive tape 3.
The Forming pipe 2 is covered with a sheath 4 consisting of polyethylene or plasticizing polyvinyl chloride or the like. The formation of the sheath 4 is carried out using the usual extruding and cladding method.
Two tension members 5, consisting of fiber-reinforced plastic or steel, brass or other such metal wire, and two rip cords 6, consisting of plastic cords, are embedded in the sheath 4. The tension members 5 are disposed opposite one another with the optical tape core laminate 1 interposed between them. The rip cords 6 are disposed opposite one another with the optical tape core laminate 1 interposed between them, and so as to be perpendicular to a line joining the two tension members 5.
In order to support and house the optical tape core laminate 1 within the forming pipe 2 without completely fixing it in place inside the pipe 2, an intermittent filling material (not shown) consisting of a soft hot-melt adhesive is employed to fill the optical cable at intermittent points along its length.
When subsequently splitting an optical cable of this design, the sheath 4 is cut open by pulling the both rip cords 6, thereby dividing the optical cable into two parts. However, it can be difficult to split the forming pipe 2 due to its high resistance to tearing, or because it adheres to the sheath 4, for example. Thus, it can take some time to expose the optical tape core laminate 1 inside. In other words, this optical cable does not always demonstrate excellent properties with respect to subsequent splitting.
The present invention was designed to resolve the problems described above, and has as its objective to provide an optical cable employing optical fiber tape cores which does not need a large amount of filling material or a long cylindrical spacer in which spiral grooves are formed. Furthermore, it is the objective of the present invention to provide an optical cable with relatively few cores which has excellent cable properties even when the optical tape core laminates are twisted in an SZ arrangement and the optical cable is bent. In addition, it is the objective of the present invention to simply and efficiently provide an optical cable which is superior with respect to ease of subsequent splitting of the cable.
An optical cable according to the present invention is provided with optical fibers, a forming pipe for housing the optical fibers, a sheath provided around the forming pipe, a pair of tension members embedded in the sheath, and a pair of rip cords similarly embedded inside the sheath, and is further characterized as follows. Namely, this forming pipe is fashioned using a plurality of tapes in such a way as to be divisible along its longitudinal direction. The rip cords are provided near the seams of this forming pipe, and the distance from the surface of the tension members to the sheath""s inner surface and to the sheath""s outer surface are both 0.3 mm or more. The distance from the center of the rip cords to the inner surface of the sheath is from 0.2-fold or greater to 1.2-fold or less than the radius of the rip cords. The distance from the surface of the rip cords to the seams of the forming pipes is 0.5 mm or less.
An optical cable according to the present invention is provided with optical fibers, a forming pipe for housing the optical fibers, a sheath provided around the forming pipe, and a pair of rip cords similarly embedded inside the sheath, and is further characterized as follows. Namely, this forming pipe is fashioned using a plurality of tapes in such a way as to be divisible along its longitudinal direction, and both ends of each of the plurality of tapes are bent toward the outside.
In this case, indicators showing the position of the ends of the plurality of tapes may be formed on the outer periphery of the sheath, and the rip cords may be provided near the seams of this forming pipe.
An optical cable according to the present invention is characterized in the provision of a cable core in which a plurality of optical fiber cores are arrayed in the form of a tape and the optical tape core laminate obtained by laminating this plurality of optical fiber tape cores is twisted in one direction or in the SZ directions; a protective tape which covers the periphery of the cable core with an interval of spacing therebetween and is not twisted (however, the cable core which is not twisted and is held in the protective tape at random when two cores type optical fiber ribbons, optical fibers, or optical fiber cores are used); a sheath which is provided around the protective tape; tension members which are embedded in the sheath; and rip cords which are similarly embedded in the sheath and are disposed near the seams of the protective tape.
In this case, the protective tape is composed of a pair of protective tape pieces, and respective rip cords are disposed near the seams of these protective tape pieces.
It is preferable that the tension members be disposed at a position which is somewhat separated from the protective tape.
The protective tapes are provided with a base and a hot-melt coating layer which is provided to the outer surface of this base. This hot-melt coating layer may be melted onto the sheath.
A water-absorbing layer may be provided to the inner surface of the protective tape""s base.
An optical cable according to the present invention is characterized in the provision of an optical tape core laminate in which a plurality of optical fiber cores are arrayed in the form of a tape and these optical fiber tape cores are laminated together; a cable core having a protective tape covering its periphery; a sheath which is provided around the cable core; and a pair of tension members which are embedded roughly opposite one another centered around the cable core. This optical cable is further characterized in that the cable core is twisted so as to alternately reverse from the left to the right at a fixed cycle, and the position at which the cable core reverses in one direction and the position at which the cable core reverses in the other direction are opposite one another and on either side of the surface which includes the pair of tension members.
In this case, it is also acceptable, in addition to the tension members to embed the rip cords inside the sheath.
The optical cable according to the present invention can be formed using a manufacturing device provided with a cylindrical inner pipe; a cylindrical nipple which is disposed outside this inner pipe with a first spacing interval therebetween, and in which tension member insertion holes and rip cord insertion holes have been formed; and a die which is disposed outside this nipple with a second spacing interval therebetween; by employing a method in which a plurality of plastic tapes are sent into this first spacing interval and are shaped into a pipe to make a forming pipe, an optical unit relayed from inside the inner pipe is housed inside this forming pipe, the tension members and the rip cords are relayed from the tension member insertion holes and the rip cord insertion holes respectively, and melted resin to form the sheath is supplied from the second spacing interval.
In this case, a plurality of projections for determining positioning may be provided to the first spacing interval in the above-described manufacturing device, and the plurality of plastic tapes can be relayed while being guided inside the first spacing interval using these various positioning projections.